Combustion apparatus

ABSTRACT

A combustion apparatus is disclosed wherein burner ports are communicated through ducts with slit-shaped air ports formed through the fins or gills of the boiler tubes immediately above the burner ports in such a way that the fresh air or the airexhaust-gas mixture may be selectively blown into the furnace. The NOx, and CO contents in the exhaust gases discharged into the surrounding atmosphere may be considerably decreased.

United States Patent Yanuki et a1.

[ COMBUSTION APPARATUS [75] Inventors: Hiroshi Yanuki, Sagamihara;

Shigeru Miyao, Yokohama, both of Japan [73] Assignee: Ishikawajima-Harima Jukogyo Kabushiki Kaisha, Tokyo, Japan Filed: June 28, 1974 Appl. No.: 484,267

[30] Foreign Application Priority Data July 12, 1973 Japan 48-83159[U] US. Cl 431/115; 110/1825; 122/235 B; 122/479 A; 431/176; 431/1'90 Int. Cl. F23L 7/00 Field of Search 431/175, 176, 116, 178, 431/190, 115; 122/235 B, 479 A; 110/1825 References Cited UNITED STATES PATENTS 6/1962 Barton 122/235 B Nov. 18, 1975 3,040,719 6/1962 Dickey 122/479 A 3,742,916 7/1973 Wessberg et a1 110/1825 Primary Examiner-Edward G. Favors Attorney, Agent, or FirmScrivener Parker Scrivener & Clarke 57 ABSTRACT A combustion apparatus is disclosed wherein burner ports are communicated through ducts with slitshaped air ports formed through the fins or gills of the boiler tubes immediately above the burner ports in such a way that the fresh, air or the air-exhaust-gas mixture may be selectively blown into the furnace. The NO and CO contents in the exhaust gases discharged into the surrounding atmosphere may be considerably decreased.

8 Claims, 5 Drawing Figures v US. Patent Nov. 18, 1975 Sheet 1 of2 3,920,377

US. Patent Nov. 18, 1975 Sheet 2 of2 3,920,377

COMBUSTION APPARATUS Smokes and gases containing pollutants such as nitrogen oxides (NO,) and sulfur oxides (S0,) recently present a serious atmospheric pollution problem. In order to overcome this problem, in the thermoelectric power plants fuels are switched to low-sulfur-content heavy oils or liquefied natural gases. Furthermore there have been proposed various improvements of the burners to overcome the above problem. Moreover, there have been proposed various improvements of the burner ports in order to reduce the pollutants such as NO in the combustion products. It is well known that in the thermoelectric power plants, the so-called off-stoichiometric combustion is carried out while the over-firing-air-ports are provided above the burner to force the air over the flames so that the production of NO, may be considerably reduced, thus resulting in the prevention of the atmospheric pollution. However, in the conventional bias combustion system employing over-firing-air-ports, an over-flring-air-port c circular in cross section is formed above each column of burner ports a as shown in FIG. 1 so that the flames blown out of the lower burner ports rise, thus resulting in the nonuniform mixture of the combustion gases with the air blown out of the over-firing-air-port 0. Consequently, smokes, soots and dusts are increased in quantity while the concentration of carbon monoxide is also increased, thus resulting in the increase in secondary atmospheric pollution. When the over-firing-air-ports are provided in a boiler, tubes b must be curved not only around the burner ports a but also around the overfiring-air-port c as shown in FIG; 1 so that the fabrication is complex and the cost is expensive. If the tubes b are bent or curved, the internal pressure loss of the tubes b will be much increased.

In view of the above, the primary object of the present invention is to form a plurality of slits in each fin interconnecting between boiler tubes so as to provide air ports, thereby overcoming the above problems.

The present invention will become more apparent from the following description of one preferred embodiment thereof taken in conjunction with the accompanying drawing in which:-

FIG. 2 is a side view of a multi-stage burner to which is applied the present invention:

FIG. 3 is a sectional view taken along the line III-III of FIG. 2;-

tube immediately above the burner, thereby forming a slit-shaped air port 8 for blowing the bias air. Even when the furnace wall is constructed by interposing a narrow plate between the adjacent bare boiler tubes :and joined to them by welding, a slit-shaped air port may be formed through the narrow interconnecting plate. The width of the slit-shaped air port is dependent upon the width of the fin or gill or plate, but the height may be suitably selected. Therefore, the heights of the slit-shaped air ports are so selected that the height of the air port immediately above the center of the burner may be greatest while the heights are gradually decreased as the slit-shaped air ports are spaced away from the center line of the burner so that the distribution of the air may be adjusted with that of the combustion gases. A bias air box 9 attached on the outer surface of the furnace wall is in communication with the slit-shaped air ports 8 and with a bias air duct 10. As shown in FIG. 5, the air discharged into the bias air duct 10 by a positive blower 22 flows into the air box 9 and then is blown into the furnace through the slitshaped air ports 8. A bias air damper 9a is disposed at the connection between the bias air box 9 and the bias air duct 10 so that the flow rate of the air may be controlled. The bias air box 9 is communicated with a burner port through an intercommunication duct 11, and a damper 1 la is disposed within the duct 1 1 so that the flow rate of the air flowing into the burner port 1 may be controlled. The burner ports 1 are communicated with a burner-air duct 12, and a burner-air separate damper 13 is disposed in each duct 12 so that the flow rate of air may be controlled. The center of the burner is indicated by X in FIGS. 2 and 3.

In case of the ordinary or normal combustion in the combustion apparatus shown in FIGS. 2-4, the burnerair separate dampers 13 are opened while the biasair inlet dampers 9a are opened very slightly and the burner-air bias dampers 11a are wide opened. Then a very small portion of the combustion air passing through the burner-air ducts 12 is supplied into the bias air boxes 9 so that the bias air boxes 9 and the structures surrounding the air boxes 9 may be cooled. A substantial portion of the combustion air is blown into the furnace (not shown) through the burner ports 1 for combustion. The control of the flow rate of the air supplied to each burner port 1 is controlled by the burner-air separate damper 13.

In order to reduce the pollutants such as NO, and in the exhaust gases discharged in the surrounding atmosphere, the burner-air separate dampers 13 are opened while the bias-air inlet dampers 9a are opened very slightly and the burner-air bias dampers 11a are wide opened. Then the air blowing into the furnace through the ducts l l and the slit-shaped air ports 8 is increased in volume while the air blown into the furnace through the burner ports 1 is reduced in volume. consequently, the off-stoichiometric combustion, i.e. the so-called bias combustion is carried out so that the contents of NO and in the exhaust gases discharged into the surrounding atmosphere may be considerably decreased.

In the boiler shown in FIG. 5, the combustion gases or products are recirculated in order to. decrease the pollutants. For this purpose, there is provided an air duct system for mixing the fresh air with the combustion gases or products and forcing the air-exhaust-gas mixture into the furnace. In FIG. 5-, reference numeral 21 denotes a gas blower; 22, a positive air blower; and 23, a furnace. Same reference numerals are used to designate the parts similar to those shown in FIGS. 2, 3 and 4, and for the sake of simplicity the gilled. boiler tubes and their fins or gills are not shown.

The six modes of operation of the boiler of the type shown in FIG. 5 are as follows:

I. In case of the normal operation, the burner-air separate dampers 13 are opened while the bias air inlet dampers 9a are' slightly opened and the burnerair bias dampers 11a are wide opened. and then the positive blower 22 is driven.

ll. The burner-air separate dampers 13 are opened while the bias-air-inlet dampers 9a are opened very slightly and the burner-air bias dampers 11a are opened, and then the positive air blower 22 is driven. As described hereinbefore with reference to FIGS. 2-4, the air blown into the furnace 23 through the burner ports 1 is reduced in volume so that the off-stoichiometric combustions, i.e. the so-called bias combustion is carried out. Consequently, the contents NQ in the exhaust gases discharged into the surrounding atmosphere are considerably decreased.

Ill. The dampers are opened as in the case of the operation l, and the positive air blower 22 and the gas blower 21 are driven. Then the so-called gas injection operation in which a part of the exhaust gases or inactive gases is mixed with combustion air and the airexhaust-gas mixture is blown through the burner ports 1 into the furnace 23 becomes possible. The contents of NO in the exhaust gases discharged into the surrounding atmosphere may be considerably decreased.

IV. The dampers are opened as with the case of the operation II, and both the positive air blower 22 and the gas blower 21 are driven. Then the bias combustion in which a part of exhaust or inactive gases is mixed with air may be carried out so that the contents of NO, in the exhaust gases may be considerably reduced.

V. The' burner-air separate dampers 13 are opened while the burner-air bias dampers 11a are closed suitable and the bias-air inlet dampers 9a are suitably opened, and both the positive air blower 22 and the gas blower 21 are driven. Then it is possible to blow the airexhaust-gas mixture whose exhaust gas ratio is lower than that of the mixture attained in the operation (lV), into the furnace 23 through the bias air boxes 9 and the slit-shaped air ports 8 so that the contents of NO in the exhaust gases may be reduced.

Vl. The burner-air separate dampers 13 are opened while the burner-air bias dampers 11a are wide opened and the bias air inlet dampers 9a are suitably opened. Both the gas blower 21 and the positive air blower 22 are driven. Then the air-exhaust-gas mixture is blown through the burner ports 1 into the furnace while only the fresh air is blown into the furnace 23 through the slit-shaped air ports 8. Consequently, the contents of NO in the exhaust gases may be also considerably decreased.

As described hereinbefore, according to the present invention, the slit-shaped air ports, i.e. air inlet ports are formed through the fins or gills of the boiler tubes immediately above the burner ports, and are communicated with the ducts so that not only the fresh air but also the air-exhaust-gas mixture may be blown into the I combustion chamber or furnace. Even though the air inlet ports are formed, the hydraulic pressure loss within the boiler tubes does not change at all, and the fabrication is simple. The air inlet ports are of a slitshaped and may be formed along the whole width or circumference of the furnace, and the heights of the slit-shaped air ports may be varied suitably. Therefore, the air may be blown in the optimum manner depending upon the distribution of the flames immediately below the slit-shaped air ports so that the uniform mixing may be atained. Therefore, not only the NO, contents are decreased but also the smokes and C are also reduced. Furthermore it is possible to selectively bias both the fresh air and the air-exhaust-gas mixture so that the freedom in operation may be much improved. When the combustion apparatus in accordance with the present invention is employed with the gas injection system, the atmospheric pollution problem may be substantially overcome. The existing boilers must be modified extensively when the conventional overfiring-air-port bias combustion system is to be employed, but the present invention may be readily applied to the existing boilers and the extensive modification or renovation is not required because the air ports are formed through the fins or gills of the boiler tubes and the scale of the works for installing the ducts and dampers is less as compared with the case when the conventional bias combustion system is employed.

What is claimed is:

1. An improvement of a combustion apparatus comprising a plurality of burner ports, a plurlity of boiler tubes provided with fins, a plurality of slit-shaped air ports formed through the fins of the boiler tubes immediately above said burner ports, and a plurality of ducts connected to said air ports.

2. An improvement as defined in claim 1 wherein one of two ducts, which are branched at the discharge port of a positive air blower is communicated with said burner ports, thereby forming a burner-air duct, while the other duct is communicated with said plurality of slit-shaped air ports, thereby forming a bias air duct; and burner-air separate dampers are disposed within said burner air duct while bias air inlet dampers are disposed within said bias air duct.

3. An improvement as defined in claim 2 wherein a burner air duct and a bias air duct are intercommunicated through an intercommunication duct at the downstream of the dampers disposed within a burner air duct and a bias air duct, respectively; and a burner air bias damper is disposed in said intercommunication duct.

4. An improvement as defined in claim 2 wherein said burner air duct and said bias air duct are intercommunicated through an intercommunication duct at the downstream of said dampers disposed within said burner air duct and said bias air duct, respectively; and a burner air bias damper is disposed in said intercommunication duct.

5. An improvement as defined in claim 2 wherein said burner air duct is communicated at the upper stream of said damper disposed in said burner air duct with an exhaust gas recirculation duct which bypasses a part of the exhaust gases discharged from a furnace or combustion chamber.

6. An improvement as defined in claim 2' wherein said burner air duct is communicated at the upper stream of said damper disposed in said burner air duct with an exhaust gas recirculation duct which bypasses a part of the exhaust gases discharged from a furnace or combustion chamber.

7. An improvement as defined in claim '3 wherein said burner air duct is communicated at the upper stream of said damper disposed within said burner air duct with an exhaust gas recirculation duct which bypasses a part of the exhaust gases discharged from a furnace or combustion chamber.

8. An improvement as defined in claim 4 wherein said burner air duct is communicated at the upper stream of said damper disposed within said burner air duct with an exhaust gas recirculation duct which bypasses a part of the exhaust gases discharged from a furnace or combustion chamber. 

1. An improvement of a combustion apparatus comprising a plurality of burner ports, a plurlity of boiler tubes provided with fins, a plurality of slit-shaped air ports formed through the fins of the boiler tubes immediately above said burner ports, and a plurality of ducts connected to said air ports.
 2. An improvement as defined in claim 1 wherein one of two ducts, which are branched at the discharge port of a positive air blower is communicated with said burner ports, thereby forming a burner-air duct, while the other duct is communicated with said plurality of slit-shaped air ports, thereby forming a bias air duct; and burner-air separate dampers are disposed within said burner air duct while bias air inlet dampers are disposed within said bias air duct.
 3. An improvement as defined in claim 2 wherein a burner air duct and a bias air duct are intercommunicated through an intercommunication duct at the downstream of the dampers disposed within a burner air duct and a bias air duct, respectively; and a burner air bias damper is disposed in said intercommunication duct.
 4. An improvement as defined in claim 2 wherein said burner air duct and said bias air duct are intercommunicated through an intercommunication duct at the downstream of said dampers disposed within said burner air duct and said bias air duct, respectively; and a burner air bias damper is disposed in said intercommunication duct.
 5. An improvement as defined in claim 2 wherein said burner air duct is communicated at the upper stream of said damper disposed in said burner air duct with an exhaust gas recirculation duct which bypasses a part of the exhaust gases discharged from a furnace or combustion chamber.
 6. An improvement as defined in claim 2 wherein said burner air duct is communicated at the upper stream of said damper disposed in said burner air duct with an exhaust gas recirculation duct which bypasses a part of the exhaust gases discharged from a furnace or combustion chamber.
 7. An improvement as defined in claim 3 wherein said burner air duct is communicated at the upper stream of said damper disposed within said burner air duct with an exhaust gas recirculation duct which bypasses a part of the exhaust gases discharged from a furnace or combustion chamber.
 8. An improvement as defined in claim 4 wherein said burner air duct is communicated at the upper stream of said damper disposed within said burner air duct with an exhaust gas recirculation duct which bypasses a part of the exhaust gases discharged from a furnace or combustion chamber. 